posted by Dustin .
What mass in grams of potassium hydroxide is contained in 500 mL of solution that has a pH of 11.5?
[OH] = 1.0 x 0^-14 / 11.5 This isn't correct. If the pH is 11.5, then the pOH = 14 - 11.5 = 2.5 = pOH and (OH^-) = 0.00316 M. It appears to me that you have Kw mixed up with pKw.
Sorry I don't quite understand can you please do a second step?
pH = 11.5
pH + pOH = 14, then
pOH = 14 - 11.5 = 2.5
If pOH = 2.5, then (OH^-) = 0.00316 M.